1. Field of the Invention
The invention relates to an instrument system for the operative correction of vertebral displacements and for the stabilizing of repositioned vertebral bodies.
2. Description of the Prior Art
In spinal column surgery it is known, for the stabilizing of lumbar spinal column segments, to use different implants and to fix the relative position of the vertebral bodies by means of these implants after a prior repositioning of the vertebral bodies. The erecting of the intervertebral space and the introduction of the required implants from the anterior is also already possible through laparoscopic operations. Since in operations of this kind not only must the distance between the vertebral bodies, which was reduced through the destruction of the intervertebral disc and which is possibly no longer even present, be restored, but vertebral bodies which are displaced relative to one another must also be brought back into their at least approximate intended position. Thus, it is necessary to make available to the surgeon an instrument system or assembly of instruments which on the one hand facilitates carrying out these difficult operations and on the other hand ensures that the danger of damage to nerve strands which exists in this critical spinal column region is largely excluded. In addition this instrument system must be suitable for carrying out laparoscopic operations in order to avoid through a minimally invasive approach from anterior the large, stressful intervention for the patient which is unavoidable in an open spinal column operation.
The object of the invention is therefore to create an instrument system of the initially named kind which can be used in particular in the framework of minimally invasive spinal column operations and which enables a sensitive and reliable repositioning of vertebral bodies with a subsequent exact positioning of implants which can be fixed in a simple manner, which can be anchored permanently in the bone of the adjacent vertebral body and which ensure the required stabilizing of the spinal column segments.
This object is substantially satisfied in accordance with the invention by correction and support devices which are formed in two parts and which are displaceable in the axial direction guided relative to one another by means of an integrated setting member, as well as by interim spacers which are adapted in their spacer dimensions to the respective correction and support devices and by perforated hollow cylinder implants which are provided with outwardly lying fixing members and which are replaceable by the correction and support devices in repositioned vertebral bodies.
The correction and support devices, which form the essential part of this instrument system, have a special importance in the framework of this instrument system. By means of these correction and support devices, which are introduced into the intervertebral disc space and in this are fixed with their one part at the one vertebral body and with their other part at the other vertebral body after the restoration of the intervertebral disc height, which is realized through the alternative introduction of spacers of increasing sizes, it is possible by means of relative displacing of the two parts to carry out the respective required repositioning sensitively and exactly. In this, two correction and support devices of this kind are introduced into the intervertebral disc space at least essentially centrally symmetrically, with it being possible to carry out the repositioning in a plurality of individual steps. Also, a reliable anchoring with the vertebral bodies which withstands the arising displacement forces is provided and the maintaining of the vertebral spacing is ensured at any time of the operation.
A preferred embodiment of the correction and support device which is intended for the introduction into an intervertebral disc space and which also represents an autonomous invention subject matter independently of the further constituents of the instrument system is characterized in that it comprises an upper and a lower carrier part; in that both carrier parts are provided at the outer side with elements for anchoring in the bordering vertebral bodies, in particular in the base and cover plates of these vertebral bodies; in that the two carrier parts are guided in a form-fitted manner with respect to one another at least in the direction of their mutual displaceability; and in that the integrated setting member consists of a setting screw which extends in the axial direction of the correction and support device, which is rotationally and axially fixedly journalled in a carrier part and which is in threaded engagement with the other carrier part.
In a special embodiment the correction and support device is formed in the shape of an approximately centrally divided cylindrical screw with a cylindrical head part which is formed at the actuation side, with the setting screw being rotatably journalled in one-half of the head part and being accessible for the actuation at the outwardly lying end surface of the head part and with the screw part halves which slide along one another being guided in a form-fitted manner with respect to one another via coupling elements.
In this way on the one hand an effortless and sensitive relative displacing of the two screw part halves is ensured and on the other hand it is ensured that the direction of the acting force is precisely predetermined by the form-fitted connection via the coupling elements and no disturbing and possibly dangerous rotation of the correction and support device as a whole can arise.
The coupling between the two screw part halves preferably takes place via a dovetail connection, and the two screw part halves have at the outer sides a cutting thread which is complementary to a through-going thread in a predetermined relative position. The cutting thread ensures a reliable anchoring of the screw part halves in the base and cover plates or the bone of the vertebral bodies which are to be displaced with respect to the one another respectively, which also enables the transmission of large forces and has the additional advantage that the cut thread can be used after the successive removal of the two correction and support devices which are used in an operation for the cylindrical implant, which is provided with a corresponding outer thread and which can be turned into the pre-cut thread. In this the flank heights of the cutting thread are preferably larger and the flank angles of the cutting thread are preferably smaller than the flank heights and the flank angles respectively of the cylinder implants, which are provided with an outer thread of the same pitch, through which a positioning of the implants can be achieved with large clamping and holding forces being achieved at the same time.
The cylindrically formed head part of the correction and support devices is provided at the end surface sides with coupling cut-outs and/or coupling extensions for an actuating member as well as with a threaded bore for connecting with the actuating member. A sleeve arrangement with a corresponding turning handle is preferably used as an actuating member, through which an actuation bar which can be coupled to the setting screw is passed. In this all parts are dimensioned and designed in such a manner that they can be introduced and handled through trocars.
The two screw thread halves have a different length in the axial direction, with it being possible for an edge-less protective plate to be molded on at the screw part end which faces away from and is more remote from the head part.
In accordance with a further embodiment of the invention the two carrier parts, which are displaceable relative to one another, are releasably coupled to areal, in particular plate-like, elements, which in turn can be fixed via projections, teeth and the like to the cover plates of the bordering vertebral bodies in the form of implants; i.e. these plate-like elements remain in the intervertebral disc space after the removal of the correction and support devices and the introduced implants are then supported at these plate-like elements. The implants, which preferably consist of hollow titanium screws, are filled with spongiosa, so that following the primary mechanical stability which is achieved after an operation the final stabilizing can take place after the growing through of the bone, for which the mentioned plate-like elements are designed to be perforated.
To be further mentioned is that a spreading arrangement can be provided between the two carrier parts of the correction and support device which can be actuated from the direction of the end surface of the head part and which can be used at least partly to achieve the required traction of the respective intervertebral disc space when the mutual guiding of the two carrier parts is correspondingly designed.